1. Technical Field
The present invention relates to an ultrasound diagnostic apparatus for forming display images of an object in periodic motion.
2. Related Art
Ultrasound diagnostic apparatuses for forming three-dimensional ultrasound images of tissue in motion, such as a heart, have been known. For example, in a known technique, ultrasonic beams are scanned in a three-dimensional region to acquire echo data, and, based on the acquired echo data, a three-dimensional ultrasound image is formed, to be displayed in real time. However, real-time display has a fundamental constraint in that a tradeoff relationship exists among the scan rate, the beam density, and the beam range.
A technique for preventing the fundamental constraint in the real-time display of three-dimensional ultrasound images has also been proposed. For example, JP 3537594B (Patent Document 1) discloses a technique in which a scanning plane is gradually displaced within the three-dimensional region in synchronization with electrocardiographic signals or the like; a plurality of sets of tomographic image data are acquired over a plurality of time phases at respective positions of the scanning planes; and the acquired tomographic image data are reconstructed to form three-dimensional image data (reconfiguration process or reconstruction process). However, difficulty is encountered in applying this technique to, for example, a fetus, from which electrocardiographic signals may not be obtained directly.
JP 2005-74225 A (Patent Document 2) discloses a technique for reconstruction by performing scanning at certain time intervals, rather than using electrocardiographic signals. However, in this technique, the motion period of a heart during data acquisition is assumed to be constant. If the motion period of a heart is not constant, the form of the heart in the reconstructed image may be distorted from the actual heart, thereby lowering reliability.
In view of the above-described background art, the inventor of the present invention has performed research and development for a technique of forming ultrasound images by means of a reconfiguration process. In particular, the inventor focused attention on the technique of forming ultrasound images of an object in unstable periodic motion, such as the heart of a fetus.